Embodiments of the invention relate generally to a radio frequency (RF) coil for use in an MR system and, more particularly, to an RF coil having improved thermal dissipation characteristics.
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, or “longitudinal magnetization”, MZ, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment Mt. A signal is emitted by the excited spins after the excitation signal B1 is terminated and this signal may be received and processed to form an image.
When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals is digitized and processed to reconstruct the image using one of many well known reconstruction techniques.
Magnetic resonance imaging systems utilize at least one radio frequency (RF) coil that applies a high-frequency magnetic field over a subject and detects a magnetic resonance signal emitted from the subject. Such transmitting and receiving may be performed by a single RF coil or by separate coils, which perform the respective transmitting and receiving operations. The RF coil or coils themselves are formed of electrically conductive members connected to various electrical components, such as capacitors, diodes, inductors, etc. When an RF coil is pulsing during operation, these electrical components may generate a significant amount of heat. Extended pulsing of the RF coil may eventually lead to highly elevated temperatures under and around the electrical components, which can potentially lead to failure of these components and/or patient discomfort within the patient bore.
The elevated temperatures near the electrical components of the RF coil are also exacerbated by poor heat dissipation in the substrate upon which those electrical components are mounted. Conventionally, a G10 FR4 electrical insulation material is used to mount the electrical components, but this insulation material is not capable of effective heat dissipation at high temperatures and is thus prone to failure due to thermal stresses over time. Other methods of reducing heat caused by extended pulsing of the RF coil may include increasing the RF tube thickness on which the RF coil is assembled, increasing the air flow over the RF coil, or reducing the air inlet temperature around the RF coil. However, these alternative techniques involve either increasing the magnet bore size or implementing a larger heat exchanger into the MR system, both of which involve a significant design alteration to other MR subsystems (e.g., magnet and/or gradient coil) and are extremely cost prohibitive.
It would therefore be desirable to produce a system and method of manufacturing an MRI RF coil comprising a low cost substrate having high thermal conductivity upon which the electrical components of the RF coil can be mounted.